2-Bromo-3-methylbutane is heated in ethanol and reacts only by E1 (SN1 products are ignored). Assume every carbocation that can form does so and that alkene formation from each is possible. How many structurally different alkenes (constitutional isomers; no geometrical isomers are possible here) can be obtained?

Answer: C

The secondary cation

CH X_{3} - CH X^{+} - CH (CH X_{3}) X_{2}

gives 3-methylbut-1-ene and 2-methylbut-2-ene. A 1,2-hydride shift gives the tertiary cation

CH X_{3} - CH X_{2} - C X^{+} (CH X_{3}) X_{2}

, which gives 2-methylbut-2-ene (again) and 2-methylbut-1-ene. The distinct alkenes are 3-methylbut-1-ene, 2-methylbut-2-ene and 2-methylbut-1-ene: three.

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Answer: C

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